Immersion Heater - PV electricity

[pauldreed]

here is schematic for control loop. I haven't finalized the +- 15v supply components so haven't included them will post full schematic when finished

I'm surprised that the value of R1 & R5 burden resistors are so high.
I'm using a CT with 3000 turns and a burden resistor value of just 240R which gives me -2.5V to +2.5V (5V p-p) when reading 5kW.
I found this handy online calculator for CT's/Burden resistors, so you can determine safe peak voltages without damaging your op amps if it helps.
Thanks for sharing your schematic, there are so many good ideas surfacing now.

 

[pmcalli]

I'm surprised that the value of R1 & R5 burden resistors are so high.
I'm using a CT with 3000 turns and a burden resistor value of just 240R which gives me -2.5V to +2.5V (5V p-p) when reading 5kW.
I found this handy online calculator for CT's/Burden resistors, so you can determine safe peak voltages without damaging your op amps if it helps.
Thanks for sharing your schematic, there are so many good ideas surfacing now.

r1 and r5 are not burden resistors they hold the i/ps to zero as a precaution if the CT's are removed. the owl ct's give 0.1v per amp which implies they have a burden resistor built in I presume for safety reasons.

 

[pauldreed]

r1 and r5 are not burden resistors they hold the i/ps to zero as a precaution if the CT's are removed. the owl ct's give 0.1v per amp which implies they have a burden resistor built in I presume for safety reasons.

Ah that makes sense. It might be worthwhile including 'nominal' burden resistors in your schematic, because if someone else builds your project using standard CT's (no internal burden resistor), the excessive voltage may damage the op amps.
I have been caught out twice now, whilst disconnecting my CT's from the PCB, have had unwelcome reminders at what high voltages are developed across the coil whilst no resistor is there to reduce it. The first time, by reaction, I snatched my hand away and cut it on an adjacent metal frame. The second time, I was miffed because I hadn't learnt from shock#1!!

 

[pmcalli]

Ah that makes sense. It might be worthwhile including 'nominal' burden resistors in your schematic, because if someone else builds your project using standard CT's (no internal burden resistor), the excessive voltage may damage the op amps.
I have been caught out twice now, whilst disconnecting my CT's from the PCB, have had unwelcome reminders at what high voltages are developed across the coil whilst no resistor is there to reduce it. The first time, by reaction, I snatched my hand away and cut it on an adjacent metal frame. The second time, I was miffed because I hadn't learnt from shock#1!!

good point I have been meaning to determine the value for a while but the only way I can think of is to put in a step impulse via a resistor and measure the initial voltage. I think all the energy monitor CT's have the burden resistor plus possibly a zener built in so joe public doesn't have your electrifying experience. I am just splitting the schematic up into a block diagram and a schematic to just cover the PCB which now incorporates the +- 15v generation so will incorporate the burden resistor into the block diagram schematic.

 

[nbown]

i have been reading though this tread with great interest, i have just a one question has any thought about using a
900W Heating Element with Thermostat the type that goes in towel rads? just pluged into the feed?
thanks

 

[suntrap]

I presume the main trouble with those is that they don't fit into the hole in a hot water cylinder.

 

[inie meanie]

i have been reading though this tread with great interest, i have just a one question has any thought about using a
900W Heating Element with Thermostat the type that goes in towel rads? just pluged into the feed?
thanks

Hi do you have a link to a product?

 

[DickiePhitt]

I'm pondering the best/easiest/most cost-effective route to inputting real time data into whatever microprocessor does the clever stuff (probably Arduino/Nanode).

The LEM CTs look expensive but I'm sure they are wonderful.

Anyone have any experience of Efergy units (cheap on Ebay) but at 90A won't they reduce accuracy?
Efergy Standard Sensor - Jackplug Fitting | eBay
Likewise I see owl CTs at a reasonable price on Amazon but cant find the spec.
OWL CMA113 Standard Sensor Fior Economy 7 Users or 3: Amazon.co.uk: Electronics
Also come across a SCT-013-030 which seems only available in USA. Anyone have any details / UK supplier?
Non-invasive AC current sensor SCT-013 (30A max) Non-invasive AC current sensor SCT-013 (30A max) [SEN005] - $9.90 : iStore, Make Innovation Easier

Finally a (silly?) thought. As I have a CC EnviR unit and additional clip-on CTs with wireless senders, which I understand operate on433MHz SRD band, the same as an Anduino shield. Could I not just pick up the existing transmitted data using the shield? Maybe a better Q for FreeEnergyForum

 

[pauldreed]

I'm pondering the best/easiest/most cost-effective route to inputting real time data into whatever microprocessor does the clever stuff (probably Arduino/Nanode).

The LEM CTs look expensive but I'm sure they are wonderful.

Anyone have any experience of Efergy units (cheap on Ebay) but at 90A won't they reduce accuracy?
Efergy Standard Sensor - Jackplug Fitting | eBay
Likewise I see owl CTs at a reasonable price on Amazon but cant find the spec.
OWL CMA113 Standard Sensor Fior Economy 7 Users or 3: Amazon.co.uk: Electronics
Also come across a SCT-013-030 which seems only available in USA. Anyone have any details / UK supplier?
Non-invasive AC current sensor SCT-013 (30A max) Non-invasive AC current sensor SCT-013 (30A max) [SEN005] - $9.90 : iStore, Make Innovation Easier

Finally a (silly?) thought. As I have a CC EnviR unit and additional clip-on CTs with wireless senders, which I understand operate on433MHz SRD band, the same as an Anduino shield. Could I not just pick up the existing transmitted data using the shield? Maybe a better Q for FreeEnergyForum

Try these CT's, they are each rated 3000:1 coil ratio, and at £16.50p FOR 2, they are tremendous value, and from my experience produce very good results. I'm well pleased with them.
As for your second point, I am doubtful. It took 2 weeks for CurrentCost to decide whether to tell me the spec of their CT's (their intellectual property rights stuff!), when I could have simply taken one to pieces and counted the turns ratio. So I am very doubtful that you would get any cooperation in establishing the communication protocol between the two. Nice lateral thinking though!

 

[nbown]

Hi do you have a link to a product?

here you go, 800W 900W Heated Towel Rail Electric Heater Element | eBay

i was thinking of having two of these, one the side and one on the top of my cylinder. just got on think of a way to kick them off. my idea is the have a current clamp on the ac output on the invertor, and when a set point for current is meet, then is would switch it on. i have 3 set points, 1x 900w, 2x900 and than the 3kw immersion.

 

[JohnBoyZ]

I moved the RCBO for the solar feed to be next to the main incomer in the cs unit and then put the CT around the the incoming meter tail and the solar feed live which are now right next to each other. second CT just goes around the solar feed live all nicely contained in the CS. My CS is a large MK sentry so there is plenty of room.

Hi, Ive been dircted to this thread from a discussion on the PV forum and have spent hours sifting through all the pages and some very interesting idea. I'm a little confused about your CT's and wondered if could you elaborate a bit on how everything is connected in your system. Do you simply have one CU with PV fed in via RCBO and immersion fed from MCB or is the immersion feed separated off from the CU. I've been trying to work out what the result is from your CT set up with up one on PV+Incoming and another on the PV?
I've currently got everything connected into the CU so have thought of putting a CT around all the house circuits (excluding immersion) and another on the PV thereby enabling me to calculate the excess power or maybe adding a Henley block to my set up to keep everything separate but is your method a cunning way to get round all that?

Its probably all very simple but its late and my brains dead
Cheers
John

 

[inie meanie]

Hi John
Have a look at Picture 1 of 5 from Power controller Sorry but it's just a sketch but it will give you the idea. The picture shows one way of connecting. The other will take the feed from the house dist board to the triac, but the circuit used is not passive but reactive , in regard that it balances the two power levels. I haven't posted that version yet but I will in a few days. I will add it to the collection of pics. I can say that I have tried the method of fitting all the cores through one ct and it's not easy. It is so much better to fit a Henley block.
Regards

 

[JohnBoyZ]

Hi John
Have a look at Picture 1 of 5 from Power controller Sorry but it's just a sketch but it will give you the idea. The picture shows one way of connecting. The other will take the feed from the house dist board to the triac, but the circuit used is not passive but reactive , in regard that it balances the two power levels. I haven't posted that version yet but I will in a few days. I will add it to the collection of pics. I can say that I have tried the method of fitting all the cores through one ct and it's not easy. It is so much better to fit a Henley block.
Regards

Hi innie,
Thanks for your diagram, it is how I envisaged things when using a Henley as it keeps every thing simple. I was intrigued with pmcalli's set up (one CT around both the the incoming meter tail and the PV and the second CT on the PV), I cant quite see how to calculate the excess PV power with that set up.
And by the way well done to you inie and all the others on this thread for coming up with so many subtly different concepts and getting them up and running, its very impressive.

EDIT:
@inie Had a look at your other diagrams and noticed your circuit diagram using a trial version of smart draw, have you tried the free circuit schematic an PCB design CAD from express PCB, I've used it, its very good and free
http://www.expresspcb.com/ExpressPCBHtm/Free_cad_software.htm



Cheers
John

 

[inie meanie]

Thanks I will down load it now and have a go.

 

[inie meanie]

PV is dead. RIP PV :- (